As a colorant for dyeing cellulose fiber or nitrogen-containing fiber, a water soluble reactive dyestuff has been usually used, and reactive dyes of various structure have been proposed so far. In dyeing the above-mentioned fiber with the conventional water soluble reactive dyestuff, a relatively low temperature of from about 60.degree. to 70.degree. C. of dyeing bath has been, in general, used.
In recent years, mixed fiber, for example, that of cellulose fiber with polyester fiber has been often used with diversification of fiber material. As a dyeing method for such mixed fiber, a so-called two-stage dyeing method is used, so that, first, the polyester fiber is dyed with a dispersion dyestuff at a high temperature of from about 120.degree. to 140.degree. C. and subsequently, the cellulose fiber is dyed with a reactive dyestuff at a low temperature of from about 60.degree. to 70.degree. C. Recently, however, a single-bath, one-step dyeing method for dyeing simultaneously the cellulose fiber and polyester fiber by combining a reaction dyestuff with a disperse dyestuff and by use of a hot dyeing bath at from 120.degree. to 140.degree. C. has been demanded.
The dyeing method has, however, a problem that, if cellulose fiber is dyed with a conventional reactive dyestuff in a hot bath at from 120.degree. to 140.degree. C., the reactivity and fixability of dyestuff to the fiber are low because of side reactions such as decomposition and a good dyed product cannot be obtained. As a dyestuff to alleviate the abovementioned defect, for example, a pyrazolone-containing reactive dyestuff represented by a formula (A) or a pyridone-containing reactive dyestuff represented by a formula (B) as set forth below has been proposed (refer to U.S. Pat. No. 4,453,945). ##STR4## If cellulose fiber is dyed by use of the above-mentioned dyestuff in a hot dyeing bath, for example, at about 130.degree. C., an effect to some extent can be obtained but the degree of exhaustion and buildup properties are insufficient and a good dyed product cannot be obtained.